if you maintain ur regular oil maintenance, why need engine flush?

imho, so far i read, old cars better not doing engine flush.

i am not sure bout this..btw is this a proven method to remove old sludge/carbon from engine?

the reason why engine flush is not recommended on old vehicle because some engine flush may

remove all the carbon, deposit, sludge which cover all the old seals. by removing them, ur old seals might get leak

and thus need a top overhaul. and who knows, the sludge might clogged the oil pump after do engine flush?

and if this is a proven method, why i didn't see any petronas, shell, sell any engine flush fluid?

well that is what i want to know about. whether it is proven safe to use or not.